CED, INU Peshawar.

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1
Chapter 16
Other Two-Terminal Devices

2. Other Two
Other Two
Other Two
Other Two
Other Two
Other Two
Other Two
Other Two-
-
-
-
-
-
-
-Terminal Devices
Terminal Devices
Terminal Devices
Terminal Devices
Terminal Devices
Terminal Devices
Terminal Devices
Terminal Devices
Schottky diode
Schottky diode
Varactor diode
Varactor diode
Power diodes
Power diodes
Tunnel diode
Tunnel diode
Photodiode
Photodiode
Photoconductive cells
Photoconductive cells
Copyright ©2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Photoconductive cells
Photoconductive cells
IR emitters
IR emitters
Liquid crystal displays
Liquid crystal displays
Solar cells
Solar cells
Thermistors
Thermistors
2
2

3. Schottky Diode
Schottky Diode
Also called Schottky
Schottky-
-barrier
barrier, surface
surface-
-barrier
barrier, or hot
hot-
-carrier
carrier diode.
Characteristics
Characteristics
(Compared with general-purpose diodes)
• Lower forward voltage drop (0.2-.63V)
• Higher forward current (up to 75A)
• Significantly lower PIV
• Higher reverse current
Faster switching rate
Copyright ©2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
• Faster switching rate
Applications
Applications
Applications
Applications
Applications
Applications
Applications
Applications
• High frequency switching
High frequency switching
High frequency switching
High frequency switching
applications
applications
applications
applications
• Low
Low
Low
Low-
-
-
-voltage high
voltage high
voltage high
voltage high-
-
-
-current
current
current
current
applications
applications
applications
applications
• AC
AC
AC
AC-
-
-
-to
to
to
to-
-
-
-DC converters
DC converters
DC converters
DC converters
• Communication equipment
Communication equipment
Communication equipment
Communication equipment
• Instrumentation circuits
Instrumentation circuits
Instrumentation circuits
Instrumentation circuits
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4. Varactor Diode
Varactor Diode
Varactor Diode
Varactor Diode
Varactor Diode
Varactor Diode
Varactor Diode
Varactor Diode
Also called a varicap
varicap, VVC
VVC (voltage-
variable capacitance), or tuning diode
tuning diode.
It basically acts like a variable
capacitor.
Copyright ©2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
capacitor.
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4

5. Varactor Diode Operation
Varactor Diode Operation
Varactor Diode Operation
Varactor Diode Operation
Varactor Diode Operation
Varactor Diode Operation
Varactor Diode Operation
Varactor Diode Operation
C(0)
A reverse-biased varactor acts like a capacitor.
Furthermore, the amount of reverse bias voltage
determines the capacitance. As VR increases the
capacitance decreases.
Copyright ©2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
where
C(0) = the capacitance with no reverse bias applied
n = 1/2 for alloy and 1/3 for diffused junctions
VT = maximum reverse bias voltage
VR = applied reverse bias voltage
n
T
R
T(VR
)
V
V
(1
C(0)
)
C
+
+
+
+
=
=
=
=
5
5

6. Varactor Diode Applications
Varactor Diode Applications
Varactor Diode Applications
Varactor Diode Applications
Varactor Diode Applications
Varactor Diode Applications
Varactor Diode Applications
Varactor Diode Applications
FM modulator
FM modulator
Automatic
Automatic-
-frequency
frequency-
-control devices
control devices
Adjustable bandpass filters
Adjustable bandpass filters
Parametric amplifiers
Parametric amplifiers
Copyright ©2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
6
6

7. Power Diodes
Power Diodes
Power Diodes
Power Diodes
Power Diodes
Power Diodes
Power Diodes
Power Diodes
• Power diodes used in high-power and high-temperature
applications, such as power rectifier circuits, must be rated
for power
• Power diodes are sometimes referred to as rectifiers
• They have the same symbol and operation as a general-
purpose diode
Copyright ©2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
purpose diode
• Power diodes are physically larger than general-purpose
diodes, and they require heat sinking.
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7

8. Tunnel Diodes
Tunnel Diodes
Tunnel Diodes
Tunnel Diodes
Tunnel Diodes
Tunnel Diodes
Tunnel Diodes
Tunnel Diodes
A tunnel diode has a negative
negative
resistance
resistance region, which means
its current decreases as the
forward-bias voltage increases.
Copyright ©2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
8
8

9. Tunnel Diodes
Tunnel Diodes
Tunnel Diodes
Tunnel Diodes
Tunnel Diodes
Tunnel Diodes
Tunnel Diodes
Tunnel Diodes
Operation
Operation
The characteristics of the tunnel diode
indicate the negative resistance region.
Note that this is only a small region of
the characteristic curve.
If the forward bias voltage is beyond the
Copyright ©2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
If the forward bias voltage is beyond the
negative resistance region, the tunnel
diode acts like a general-purpose diode.
If the forward bias voltage is in the
negative resistance region then the
diode can be used as an oscillator.
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9

10. Tunnel Diode Applications
Tunnel Diode Applications
Tunnel Diode Applications
Tunnel Diode Applications
Tunnel Diode Applications
Tunnel Diode Applications
Tunnel Diode Applications
Tunnel Diode Applications
High frequency circuits
High frequency circuits
Oscillators
Oscillators
Switching networks
Switching networks
Pulse generators
Pulse generators
Copyright ©2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Pulse generators
Pulse generators
Amplifiers
Amplifiers
10
10

11. Photodiodes
Photodiodes
Photodiodes
Photodiodes
Photodiodes
Photodiodes
Photodiodes
Photodiodes
A photodiode conducts when light is applied to
the junction.
Operation
Operation
The photodiode is operated in reverse
bias. When light of a particular
wavelength strikes the junction it
conducts. The higher the intensity of light
Copyright ©2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Applications
Applications
• Instrumentation circuits as a sensor
• Alarm system sensor
• Detection of objects on a conveyor belt
conducts. The higher the intensity of light
(measured in foot-candles), the higher the
conduction through the photodiode.
Note that the diode conducts somewhat with no
light applied, this is called the dark current.
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11

12. Photoconductive Cells
Photoconductive Cells
Photoconductive Cells
Photoconductive Cells
Photoconductive Cells
Photoconductive Cells
Photoconductive Cells
Photoconductive Cells
Operation
Operation
A photoconductive cell varies
resistance with intensity of
light.
Like a common resistor, a
Copyright ©2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Like a common resistor, a
photoconductive cell has no
polarity and can be placed into
the circuit in either direction.
Applications
Applications
• Light/darkness detection
• Controlling intensity of lighting
systems
12
12

13. IR Emitters
IR Emitters
IR Emitters
IR Emitters
IR Emitters
IR Emitters
IR Emitters
IR Emitters
These are diodes that emit IR (infrared
radiation)
Operation
Operation
Operation
Operation
Operation
Operation
Operation
Operation
IR emitter produce infrared radiation
when forward biased. The higher the
forward bias current, the greater the
intensity of infrared radiation.
Copyright ©2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
The radiation pattern can vary from
widely dispersed to a very narrow,
focused beam.
Applications
Applications
•
• Card readers
Card readers
•
• Shaft encoders
Shaft encoders
•
• Intrusion alarms
Intrusion alarms
•
• IR Transmitters
IR Transmitters
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14. Liquid Crystal Displays (LCDs)
Liquid Crystal Displays (LCDs)
Liquid Crystal Displays (LCDs)
Liquid Crystal Displays (LCDs)
Liquid Crystal Displays (LCDs)
Liquid Crystal Displays (LCDs)
Liquid Crystal Displays (LCDs)
Liquid Crystal Displays (LCDs)
There are two varieties—those with a light background and dark display or
those with a dark background and light display.
Operation
Operation
The background is either light or dark, when a voltage is
applied to a segment then the alphanumeric display is visible.
The amount of voltage necessary for display varies
Copyright ©2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
The amount of voltage necessary for display varies
depending on the type of display, from 2 to 20V.
Low power LCDs require less power than LEDs. But LEDs
have faster response times and longer life.
Applications
Applications
• Digital clocks
• Digital thermometers
• Odometers
14
14

15. Solar Cells
Solar Cells
Solar Cells
Solar Cells
Solar Cells
Solar Cells
Solar Cells
Solar Cells
Solar cells produce a voltage
when subjected to light
energy.
The greater the light
Copyright ©2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
The greater the light
intensity, the greater amount
of voltage produced.
15
15

16. Thermistors
Thermistors
Thermistors
Thermistors
Thermistors
Thermistors
Thermistors
Thermistors
Thermistors are resistors whose value
changes with temperature.
Operation
Operation
Thermistors are negative-coefficient
devices—their resistance decreases as the
temperature increases.
Copyright ©2009 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
temperature increases.
Applications
Applications
• Sensors in instrumentation circuits
• Temperature correction circuitry
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